The long-term objectives of this project are to characterize the fetal cerebral metabolic and behavioral response to the application of sound during physiologic and pathologic conditions. Although stimulation by sound is rapidly gaining popularity in the clinical obstetric community as a means of fetal assessment, very little is known about its effects on the fetus or the fetal brain. Recent data have suggested that sound stimulation causes marked increases in fetal glucose metabolism throughout the cerebral cortex. In addition, studies in the normally oxygenated adult suggest that stimulation-induced increases in glucose consumption are metabolized anaerobically. Application of sound to the fetus may thus result in local lactate production by the fetal brain which may be deleterious to the fetus. Fetal sheep will be chronically catheterized and microsphere measurements of cerebral blood flow will be made with and without the application of a sound stimulus. Arteriovenous differences for glucose, oxygen, and lactate will be obtained and cerebral net fluxes calculated. In addition, the behavioral response will be assessed by measurement of heart rate, electroencephalogram, and limb and nuchal electromyograms. The development of the cerebral response will be investigated in terms of gestational age. Fetal habituation to the stimulus will be characterized and the metabolic consequences of habituation will be explored. The fetal response to sound will be determined during and after ischemia, a time when a dissociation between behavioral and metabolic responses has been observed in the adult. The goals are a.) to build a base of knowledge of the cerebral metabolic and behavioral responses to sound in order to more fully evaluate the clinical utility and safety of the use of sound as a tool to diagnose fetal well-being and b.) to utilize sound stimulation as a model of sensory activation to determine the contribution of anaerobic metabolism to total glucose consumption during physiologic and pathological circumstances as a result of stimulation.